Commodore VIC-20 User Manual page 189

Chapter 6: Graphics
175
example, the following short program will display a drawing of a car on the
screen:
100 PRINT
":'l"
200
PRINT "~ "
300 PRINT "/ , "
400 PRINT
"I I "
500 PRINT "0 0 "
One of the advantages of creating displays with PRINT statements is
that you can doodle on the screen in immediate mode until you're satisfied
with your player, then build the PRINT statements around it. This is how we
built the car in the program above. Let's look at the process step by step,
using a simpler example.
Step 1: Clear the screen. Use the
SHIFT
and
CLR/HOME
keys (Figure 6-3a).
Step 2: Draw the top half of the diamond. Type
SHIFT-N,
then
SHIFT-M
(Figure 6-3b). Don't press
RETURN;
if you do, the VIC will try to
execute what you just typed and print a READY message on your
picture. (If you type any nongraphics characters, you may also get a
?SYNTAX ERROR message.) To avoid this, type
SHIFT-RETURN.
The cursor will still move down to the beginning of the next line, but
the VIC will not try to execute your picture.
Step 3: Draw the bottom half of the diamond. Type
SHIFT-M
and
SHIFT-N
to complete the diamond (Figure 6-3c).
Step 4: Home the cursor. Press the
CLR/HOME
key without pressing the
SHIFT
key (Figure 6-3d).
Step 5: Insert four spaces with the
INST / DEL
key. This leaves room for a line
number, a "?" for PRINT, and a double quote to start a string (Figure
6-3e).
Step 6: Type in the PRINT statement. Enter the line number (10), a ques-
tion mark, and the double quote (Figure 6-3j).
Step 7: Press
RETURN.
Don't use
SHIFT
this time. BASIC stores the first
line of the diamond as a program line. Repeat steps 5 through 7 for the
second line of the drawing, using a line number of 20 this time.
You now have a program that can be RUN to display the diamond
drawing. This method can be used to reproduce almost anything you can
sketch on the screen, from a simple square to a complex picture. The only